a) Field of the Invention
The present invention relates to a data communications network system in which a communications signal having a data identification information is transmitted and received by a plurality of data transmission and reception units which belong to different local area networks (LANs).
b) Description of the Related Art
It is well known that a plurality of units (so-called, nodes) are connected to computer communications network and multiplexing of communications of data are carried out between the units. Such a computer communications network as described above is intervened between pieces of electronic equipments mounted in an automotive vehicle.
For example, a vehicular velocity control unit to adaptively control a vehicular velocity, a car navigation unit to inform a vehicular occupant of a vehicular information, an audio unit, and so forth are interconnected via a communications line. A specific ID (Identification) code is assigned to the communications signal transmitted from each unit on the communications line.
When the communications signal is applied to a broadcast communication system adopted LAN (Local Area Network) such as a CAN (Controller Area Network), an ID filter is provided in each data reception unit on a presumption that no doubled ID codes is present so that only the data having the required ID code is selectively received.
The ID code of the transmission data to be retrieved in the corresponding unit(s) is previously set and, if the ID code of the transmitted data on the communications line is the same as the ID code present in the corresponding unit, the transmitted data is retrieved into the unit.
In the above-described computer communications network, a data on a road gradient value calculated by the car navigation unit is, for example, transmitted to the vehicular velocity unit in which a down-shift control for a gear ratio of an automatic transmission is carried out on the basis of the transmitted road gradient value data.
Various kinds of transmission data are transmitted from the unit connected to the communications line with the individual ID codes attached thereto.
To transmit only the road gradient value data to the vehicular velocity control unit without failure, a gateway (module) is interposed in communications line between the vehicular velocity control unit and another communications unit. The gateway (module) is used to interconnect different systems or different networks. The gateway module, in the above-described example, transmits only the road gradient value data from among the data to be transmitted from the network including the navigation unit to the other network including the vehicular velocity control unit.
However, even if a transmission/reception function of each unit is normal, a trouble such as a short-circuiting occurs in a circuitry to supply the transmission data on the communications line so that an erroneous ID code which is different from a normal ID code that the transmission data naturally has is often attached onto the transmission data and is transmitted onto the communications line.
At this time, the unusual ID code may be considered to be the same as the ID code attached to the road gradient value data. If such a trouble as described above occurs in an audio unit, the audio data having accidentally the same ID code as the road gradient value data passes through the gateway module so as to be transmitted to the vehicular velocity control unit.
This audio data has the same ID code as the road gradient value data so as to be retrieved into the vehicular velocity control unit. Accordingly, an erroneous operation in the vehicular velocity control unit may occur since the retrieved data is not the road gradient value data that the vehicular velocity control unit should receive.